Modern trucks include air compressors which are used to charge an air tank from which air-powered systems, such as service brakes, windshield wipers, air suspension, etc., can draw air. Water vapor in the ambient air is concentrated at the outlet of the compressor and generally condenses as the compressed air cools. An air dryer is typically disposed between the compressor and the air tank. The air dryer removes liquid and water vapor from compressor discharge air before the air is provided to the air tank. Typical air dryers include a desiccant type filtration system. The air dryer provides clean, dry air to the reservoir.